Power factor control systems and methods

ABSTRACT

A boost converter comprises an inductance that receives an input signal. A switch controls current supplied via the inductance to a load. A power factor control module comprises a mode control module that selects an operating mode of the boost converter and a switch control module that switches the switch at a frequency. The frequency is equal to a first frequency when the mode control module selects a continuous mode and equal to a second frequency when the mode control module selects a discontinuous mode. The first frequency is greater than the second frequency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/038,630, filed Mar. 21, 2008. This application is acontinuation-in-part of U.S. patent application Ser. No. 11/977,869filed on Oct. 26, 2007, which is a continuation of U.S. Pat. No.7,292,013 issued on Nov. 6, 2007. The disclosures of theabove-identified applications and patents are incorporated herein byreference in their entirety.

This application may be related to U.S. Pat. No. 7,266,001, issued onSep. 4, 2007, which is incorporated herein by reference in its entirety.

FIELD

The present disclosure generally relates to power factor correctioncontrol systems and methods.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

A load may appear to a power supply as a resistive impedance, aninductive impedance, a capacitive impedance, or a combination thereof.When the current passing to the load is in phase with the voltageapplied to the load, the power factor approaches one.

When the power factor is less than one, transmitted power can be wasted(due to phase mismatch between current and voltage) and/or noise may beintroduced into the power line. To reduce noise and improve efficiency,power supplies generally use power factor correction (PFC) circuits tocontrol the phase of the current waveform relative to the phase of thevoltage waveform.

Referring now to FIG. 1, a conventional boost converter 10 includesrectifier 15, which receives alternating current (AC) power. Inputcurrent I_(in) passes through inductor 20 and part of input currentI_(in) passes through diode 50 (having a capacitor/filter 60 at itsoutput) before being applied to load 70.

Power factor controller 30 controls the current flowing through inductor20 by turning switch 40 on and off in response to an AC voltage-sensinginput 12, a DC output voltage 72, a sensed power conversion current froma second inductor coil 25, and a feedback current via node 34. Whenswitch 40 is on, current 22 generally flows through inductor 20 (therebystoring some energy in inductor 20) and then through switch 40 toground. When switch 40 is off, current 52 may flow through diode 50 andsome charge may collect on capacitor/filter 60. Generally, current flow22 through inductor 20 is significantly reduced or even prevented whenthe switch 40 is off.

Referring now to FIG. 2, an AC voltage V received by boost converter 10is shown. Input voltage V is a rectified half-sine wave of the ACwaveform input. However, due to the on/off cycles of switch 40(controlled by power factor controller 30 in FIG. 1), the currentwaveform I in FIG. 2 has a sawtooth pattern. After passing the sawtoothwaveform I through a low-pass filter (e.g., high frequency bypasscapacitor/filter 60 in FIG. 1), the input current waveform resembles theinput AC voltage at the input of rectifier 15.

The PF for the conversion approaches 1 under most conditions,particularly those conditions where the loading power is sufficientlyhigh to allow an appreciable average input current to continuously passthrough inductor 20. This mode is known as the “average current mode” or“continuous mode” of operation for boost converter 10.

The PFC for a boost converter generally has two parameters defined by aspecification: (1) PF, and (2) total harmonic distortion (or THD). THDrefers to distortion caused generally by higher order harmonics. For a60 Hertz (Hz) AC signal, higher order harmonics are located at 120 Hz,180 Hz, or other n*60 Hz values, where n is an integer of 2 or more.Generally, the higher the THD, the lower the efficiency. Harmonicdistortion can saturate inductor 20 in boost converter 10. Moreover, ifthe THD is sufficiently high, noise can be fed back onto the AC powerlines 12-14, which is undesirable.

Referring now to FIG. 3A, a low-power and/or low-voltage portion 120 ofthe voltage and current waveforms of FIG. 2 are shown. The voltagewaveform V is the voltage at the output of rectifier 15 (see FIG. 1).The current waveform I is the input current I_(in) passing throughinductor 20. When switch 40 in FIG. 1 is turned on at time to, current Iincreases in a substantially linear manner, as shown by slope 122.Switch 40 is on for a period of time determined by power factorcontroller 30. At the end of this time (point 124 on the currentwaveform I in FIG. 3A), switch 40 turns off and current I decreases in asubstantially linear manner. Switch 40 then is turned on again by powerfactor controller 30 (see FIG. 1) after a period of time t_(s)-t₀, alsodetermined by power factor controller 30.

When current I=0 (i.e., I_(o), the current value during “zero currentperiod” 126 in FIG. 3A), the average current or continuous mode ofoperation has a potential distortion issue. The THD cannot be controlledduring the zero current period 126 of waveform portion 120 because thereis no current flowing through inductor 20 of FIG. 1.

The discontinuous mode of operation of boost converter 10 occurs duringperiods of time where switch 40 is turned on and off for lengths of timesufficient for zero current periods to occur. The critical mode ofoperation occurs when current waveform I (see FIG. 3A) is at or nearzero (I_(o)). It is desirable to maximize the amount of time that theinductor current I_(in) is above zero (see FIG. 1) and to minimize thezero current periods (e.g., zero current period 126 of FIG. 3A).

Referring now to FIG. 3B, ideally t_(s) would occur at a point in timewhen current I crosses I₀ (the “I=0” axis), zero current period 126would have a duration as close to 0 units of time as possible, andswitch 40 (see FIG. 1) would be turned on essentially immediately bypower factor controller 30 (see FIG. 1) after current waveform portion134 intersects I₀ (see FIG. 3B). When this occurs, current waveformportion 136 increases soon after current waveform portion 134 intersectsI_(o) and current to flow through inductor 20 (see FIG. 1) substantiallycontinuously. The switch 40 should not be turned on too soon (i.e.,before current waveform portion 134 in FIG. 3B intersects I₀). When thisoccurs, the average input current may increase at too high a rate, whichcould cause the input current waveform phase to move out of alignmentwith the input voltage waveform phase.

One conventional approach detects the input current I_(in) flowingthrough inductor 20 in FIG. 1. A second inductor coil 25 magneticallycoupled to the inductor 20 senses the current I_(in) flowing throughinductor 20. However, this approach suffers from latency when sensingthe current in another coil. The latency introduces some positive lengthof time in the zero current period 126 (see FIG. 3A) and noise back intothe AC power line 12-14. Also, the second inductor coil 25 adds someexpense to manufacturing power factor controller 30 and necessitates atleast one dedicated differential pin on power factor controller 30 toreceive information from second inductor coil 25.

Another approach attempts to sense the current at node 34 in FIG. 1.However, the current and voltage values at node 34 are relatively low inthe critical mode of operation. As a result, error signals based on themeasurement are relatively inaccurate. Also, determining the current atnode 34 would require power factor controller 30 to have a relativelyhigh sampling rate (i.e., >>1 sample taken every 1/[t_(s)−t₀] seconds)in the critical mode, and the sampling resolution should be relativelyhigh to avoid turning switch 40 on too fast or too slow.

SUMMARY

A boost converter comprises an inductance that receives an input signal.A switch controls current supplied via the inductance to a load. A powerfactor control module comprises a mode control module that selects anoperating mode of the boost converter; and a switch control module thatswitches the switch at a switching frequency. The switching frequency isequal to a first frequency when the mode control module selects acontinuous mode and equal to a second frequency when the mode controlmodule selects a discontinuous mode. The first frequency is greater thanthe second frequency.

In other features, the switch control module determines the switchingfrequency independently of measurement of current through theinductance. The power factor control module further includes: a phasedetecting module that determines a period of the input signal; a peakvoltage determining module that senses a peak voltage of the inputsignal; and an on-time module that provides an on-time of the switch.The power factor control module further comprises an off-time modulethat calculates an off-time of the switch based on the period, theon-time and the peak voltage. The off-time module calculates theoff-time independently of measurement of current flowing through theinductance. The phase detecting module comprises a zero-crossing modulethat detects zero-crossing of a voltage of the input signal.

In other features, when the mode control module selects the continuousmode, the boost converter transitions from the discontinuous mode to thecontinuous mode based on the zero-crossing. When the mode control moduleselects the discontinuous mode, the boost converter transitions from thecontinuous mode to the discontinuous mode based on the zero-crossing.The phase detecting module further determines a phase of the inputsignal. The first frequency is greater than a boundary frequency and thesecond frequency is less than the boundary frequency. The boundaryfrequency is based on the phase of the input signal.

In other features, the boundary frequency is based on:

f _(c)=0.25*(V _(p) ²)*(1−V _(p)*sin(θ)/V _(o))/(P _(o) *L)

where f_(c) is said boundary frequency, θ is said phase, V_(p) is a peakvoltage of said input signal, V_(o) is an output voltage of said powerconverter, P_(o) is an output power of said power converter, and L is avalue of said inductance.

In other features, the boundary frequency is based on a peak value ofthe input signal, an output power of the boost converter, and a value ofthe inductance. The boundary frequency is a product of a maximumthreshold frequency and a first value. The maximum boundary frequency isbased on the peak voltage of the input signal, an output power of theboost converter, and a first inductance value of the inductance. Thefirst value is based on the peak voltage of the input signal and theoutput power of the boost converter.

A power factor controller comprises a mode control module that selectsan operating mode of a power converter and a switch control module thatswitches a switch at a switching frequency to control current suppliedvia an inductance to a load. The switching frequency is equal to a firstfrequency when the mode control module selects a continuous mode. Theswitching frequency is equal to a second frequency when the mode controlmodule selects a discontinuous mode. The first frequency is greater thanthe second frequency. The switch control module determines the switchingfrequency independent of measurement of current through the inductance.A method for operating a boost converter comprises providing a switchthat controls current supplied via an inductance to a load; selecting anoperating mode of the boost converter; switching the switch at aswitching frequency; and setting the switching frequency equal to afirst frequency when operating in a continuous mode and equal to asecond frequency when operating in a discontinuous mode. The firstfrequency is greater than the second frequency.

In other features, the method further comprises determining theswitching frequency independently of measurement of current through theinductance. The method further includes determining a period of an inputsignal; sensing a peak voltage of the input signal; and providing anon-time of the switch.

In other features, the method includes calculating an off-time of theswitch based on the period, the on-time and the peak voltage. Theoff-time is calculated independently of measurement of current flowingthrough the inductance. The method further includes detectingzero-crossing of a voltage of the input signal. When the continuous modeis selected, the boost converter transitions from the discontinuous modeto the continuous mode based on the zero-crossing. When thediscontinuous mode is selected, the boost converter transitions from thecontinuous mode to the discontinuous mode based on the zero-crossing.

In other features, the method includes detecting a phase of the inputsignal. The first frequency is greater than a boundary frequency and thesecond frequency is less than the boundary frequency. The boundaryfrequency is based on the phase of the input signal. The boundaryfrequency is based on:

f _(c)=0.25*(V _(p) ²)*(1−V _(p)*sin(θ)/V _(o))/(P _(o) *L)

where f_(c) is said boundary frequency, θ is said phase, V_(p) is a peakvoltage of said input signal, V_(o) is an output voltage of said powerconverter, P_(o) is an output power of said power converter, and L is avalue of said inductance.

In other features, the boundary frequency is based on a peak value ofthe input signal, an output power of the boost converter, and a value ofthe inductance. The boundary frequency is a product of a maximumboundary frequency and a first value, wherein the maximum boundaryfrequency is based on the peak voltage of the input signal, an outputpower of the boost converter, and a first inductance value of theinductance. The first value is based on the peak voltage of the inputsignal and the output power of the boost converter.

A method for operating a power factor controller comprises selecting anoperating mode of a power converter; switching a switch at a switchingfrequency to control current supplied via an inductance to a load;setting the switching frequency equal to a first frequency when the modecontrol module selects a continuous mode; and setting the switchingfrequency equal to a second frequency when the mode control moduleselects a discontinuous mode. The first frequency is greater than thesecond frequency. The switch control module determines the switchingfrequency independent of measurement of current through the inductance.

A boost converter comprises inductance means for providing inductanceand for receiving an input signal; switching means for controllingcurrent supplied via the inductance means to a load; and power factorcontrol means for controlling a power factor of the boost convertercomprising mode control means for selecting an operating mode of theboost converter and switch control means for setting a switchingfrequency of the switching means equal to a first frequency when themode control means selects a continuous mode and equal to a secondfrequency when the mode control means selects a discontinuous mode. Thefirst frequency is greater than the second frequency.

A power factor controller comprises mode control means for selecting anoperating mode of a power converter; and switch control means forswitching a switch at a switching frequency to control current suppliedvia an inductance means to a load. The switch control means sets theswitching frequency equal to a first frequency when the mode controlmeans selects a continuous mode and the switch control means sets theswitching frequency equal to a second frequency when the mode controlmeans selects a discontinuous mode. The first frequency is greater thanthe second frequency. The switch control means determines the switchingfrequency independent of measurement of current through the inductancemeans.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a diagram showing a conventional boost converter.

FIG. 2 is a graph depicting voltage and current waveforms at particularnodes in the conventional boost converter of FIG. 1.

FIGS. 3A-3B are graphs depicting a low-voltage and low-current portionof the waveforms of FIG. 2.

FIG. 4 is a diagram of an exemplary boost converter according to thepresent disclosure.

FIGS. 5-6 are graphs of low-voltage and low-current waveforms useful forexplaining the operation of the exemplary boost converter of FIG. 4.

FIG. 7 is a graph depicting voltage and current waveforms for bothdecreasing and increasing values of the voltage half-sine wave usefulfor explaining the operation of the exemplary boost converter of FIG. 4.

FIG. 8 is a diagram of another exemplary power factor controlleraccording to the present disclosure.

FIG. 9 is a functional block diagram of an alternate exemplary powerfactor controller according to the present disclosure.

FIG. 10A illustrates a method for controlling switching frequency basedon a mode of the boost converter.

FIG. 10B illustrates a method for controlling transitions between modesbased on voltage zero crossings.

FIG. 11 illustrates a switching frequency ratio as a function of AC linephase for the continuous and discontinuous modes.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. While the disclosure will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the disclosure to these embodiments. On the contrary, thedisclosure is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of thedisclosure as defined by the appended claims. Furthermore, in thefollowing detailed description of the present disclosure, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present disclosure. However, it will be readilyapparent to one skilled in the art that the present disclosure may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the presentdisclosure.

Some portions of the detailed descriptions which follow are presented interms of processes, procedures, logic blocks, functional blocks,processing, and other symbolic representations of operations on databits, data streams or waveforms within a computer, processor, controllerand/or memory. These descriptions and representations are generally usedby those skilled in the data processing arts to effectively convey thesubstance of their work to others skilled in the art. A process,procedure, logic block, function, operation, etc., is herein, and isgenerally, considered to be a self-consistent sequence of steps orinstructions leading to a desired and/or expected result. The stepsgenerally include physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofelectrical, magnetic, optical, or quantum signals capable of beingstored, transferred, combined, compared, and otherwise manipulated in acomputer, data processing system, or logic circuit. It has provenconvenient at times, principally for reasons of common usage, to referto these signals as bits, waves, waveforms, streams, values, elements,symbols, characters, terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare associated with the appropriate physical quantities and are merelyconvenient labels applied to these quantities. Unless specificallystated otherwise and/or as is apparent from the following discussions,it is appreciated that throughout the present application, discussionsutilizing terms such as “processing,” “operating,” “computing,”“calculating,” “determining,” “manipulating,” “transforming,”“displaying” or the like, refer to the action and processes of acomputer, data processing system, logic circuit or similar processingdevice (e.g., an electrical, optical, or quantum computing or processingdevice), that manipulates and transforms data represented as physical(e.g., electronic) quantities. The terms refer to actions, operationsand/or processes of the processing devices that manipulate or transformphysical quantities within the component(s) of a system or architecture(e.g., registers, memories, other such information storage, transmissionor display devices, etc.) into other data similarly represented asphysical quantities within other components of the same or a differentsystem or architecture.

Furthermore, for the sake of convenience and simplicity, the terms“data,” “data stream,” “waveform,” and “information” are generally usedinterchangeably herein, but are generally given their art-recognizedmeanings. Also, for convenience and simplicity, the terms “connectedto,” “coupled with,” “coupled to” and “in communication with” may beused interchangeably (which terms may also refer to direct and/orindirect relationships between the connected, coupled and/orcommunication elements unless the context of the term's useunambiguously indicates otherwise), but these terms are also generallygiven their art-recognized meanings. As used herein, the term module,circuit and/or device refers to an Application Specific IntegratedCircuit (ASIC), an electronic circuit, a processor (shared, dedicated,or group) and memory that execute one or more software or firmwareprograms, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality. As used herein, thephrase at least one of A, B, and C should be construed to mean a logical(A or B or C), using a non-exclusive logical or.

The present disclosure concerns a circuit, system, method, and softwarefor power factor correction and/or control. The present disclosuregenerally takes a computational approach to reducing and/or minimizingzero current periods in the critical mode of boost converter operation.One inventive circuit is a power factor controller, comprising (a) acircuit configured to determine and/or identify (i) a period of aperiodic power signal and (ii) a length of time from a beginning of theperiod during which a potential is applied to a power conversion switch;(b) a voltage calculator configured to determine at least a peak voltageof the periodic power signal; and (c) logic configured to calculate atime period to open the switch in response to (i) the length of time,(ii) the power signal period, and (iii) the peak voltage. The systemgenerally comprises the present power factor controller and a switchthat it controls, although a further aspect of the system relates to apower converter comprising such a system and an inductor or other meansfor storing energy from a periodic power signal, such as an AC powersignal.

A further aspect of the disclosure concerns a method of correctingand/or controlling a power factor and/or controlling a power conversion.The method generally comprises (1) storing energy from a periodic powersignal in a power converter in response to application of a potential toswitch in electrical communication with the power converter; (2)calculating a time period to open the switch from (i) an initial lengthof time during which a potential is applied to the switch, (ii) a periodof the periodic power signal, and (iii) a peak voltage of the periodicpower signal; and (3) opening the switch during the time period. Thesoftware comprises a processor-readable or -executable set ofinstructions generally configured to implement the present method and/orany process or sequence of steps embodying the inventive conceptsdescribed herein.

The disclosure, in its various aspects, will be explained in greaterdetail below with regard to exemplary embodiments.

An Exemplary Boost Converter

In one aspect, the present disclosure relates to a power converter,comprising the present power factor controller (described in greaterdetail below), an inductor configured to store energy from a periodicpower signal, and a power conversion switch configured to charge theinductor when a potential is applied to the switch. Generally, theswitch is controlled by the present power factor controller, and theperiodic power signal is either an alternating current (AC) power signalor a rectified AC power signal. In one implementation, the powerconverter is an AC-DC boost converter.

In various embodiments, the power converter may further comprise a diodeconfigured to receive an output from the inductor and provide an outputvoltage to a load; a ripple filter coupled to an output of the diode;and/or a rectifier configured to rectify an alternating current powersignal. In one embodiment, the periodic power signal comprises an outputof the rectifier (e.g., it is a rectified AC power signal).

In other embodiments, the inductor converts the periodic power signal(e.g., the AC signal) into a substantially constant power signal (e.g.,a DC signal); and/or the switch may be configured to (i) provide a powerconversion current to the inductor when a potential is applied to it(e.g., when it is closed) and/or (ii) reduce, eliminate or prevent apower conversion current from passing through the inductor when theswitch is open.

The operation of the present power factor controller and power convertermay be best explained with reference to an exemplary embodiment. FIG. 4shows a first exemplary embodiment of a boost converter 200, includingfour-way rectifier 210 receiving alternating current power supply ACfrom power lines 212 and 214, inductor 220, exemplary power factorcontroller 230, and switch 240. Boost converter 200 may further includecurrent feedback resistor 235, diode 250, and capacitor/filter 260, thenode 272 to which may also be in communication with load 270. Similarlyto the conventional power factor controller 30 of FIG. 1, power factorcontroller 230 of FIG. 4 effectively controls the current flowingthrough inductor 220 by turning switch 240 on and off in response to ACpower line 212, DC output voltage 272, and feedback current node 234.However, the present power factor controller 230 computes the length oftime that switch 240 remains off in order to reduce or minimize zerocurrent periods, and does not require a second inductor to sense whenthe input current through inductor 220 is zero.

For example, in FIG. 4, when switch 240 is on, a current generally flowsthrough inductor 220 thereby storing some energy in inductor 220. Whenswitch 240 is off, current may flow through diode 250 and some chargemay collect in capacitor/filter 260, but generally, current flow throughinductor 220 is significantly reduced or prevented. Diode 250 is thusconfigured to (i) receive an output from inductor 220 and (ii) passcurrent unidirectionally from the inductor output to a substantiallyconstant output voltage (generally applied to a load 270).

One object of the disclosure is to compute or calculate the length oftime that switch 240 is off (“t_(off)”) that results in a zero currentthrough inductor 220. If one can compute or calculate (“t_(off)”), thenone can determine when to turn switch 240 back on in a manner minimizingthe zero current period. The disclosure focuses on a power factorcontroller configured to conduct such calculations.

FIG. 5 shows current and voltage waveforms for the exemplary boostconverter 200 of FIG. 4 in a critical current mode of operation. Switch240 is turned on at time to, causing the current I flow through inductor220 to increase at a substantially linear rate (e.g., see currentwaveform section 310 in FIG. 5). Switch 240 remains on for apredetermined length of time t_(on), where the predetermined length oftime may be programmed into a memory unit in power factor controller 230(see FIG. 4) or may be calculated, computed or determined conventionallyby power factor controller 230 in response to one or more conventionalinputs (e.g., a current or voltage input from AC power line 212, a powerconversion feedback from output voltage V_(out) node 272 and/or feedbackcurrent node 234, etc.). After time t_(on), power factor controller 230turns switch 240 off, and current waveform I decreases at asubstantially linear rate until current I=0 (e.g., see current waveformsection 320 in FIG. 5). The length of time that switch 240 is off forcurrent I to reach 0, t_(off), can be computed or calculated usingrelatively simple triangulation techniques from a number of knownparameters, including t_(on), the AC input voltage and the peak AC inputvoltage V_(p) on AC power line 212, and the output voltage V_(out) atnode 272. It is well within the abilities of one skilled in the art todesign and use logic configured to compute or calculate t_(off) fromthese known parameters, as will be apparent to those skilled in the artfrom the following discussion.

The triangulation approach to determining t_(off) is relativelystraight-forward. Referring to FIG. 5, the slope of increasing currentwaveform section 310 is simply the voltage V_(in) at node 216 divided bythe inductance L of inductor 220. Similarly, the slope of decreasingcurrent waveform section 320 is simply the output voltage V_(out) (atnode 272) minus V_(in) (node 216), divided by L. Current waveformsections 310 and 320 each form the hypotenuse of two right triangles,the abscissa of which is the current I_(in) through inductor 120 at timet_(on), and the respective ordinates of which are t_(on) and t_(off).From these relationships, we can calculate t_(off). Mathematically,

Slope(310)=V _(in) /L   [1]

Slope(320)=(V _(out) −V _(in))/L   [2]

t _(off) =t _(on) * V _(in)/(V _(out) −V _(in))   [3]

The output voltage V_(out) is generally predetermined and/or known bydesign; e.g., it has a specified, substantially constant value (forexample, 450 V), although there will be some minor fluctuations in theactual value due to small ripples, the source(s) of which are known tothose skilled in the art, but which as a percentage of V_(out) areinsignificant and/or negligible. Thus, for purposes of computingt_(off), V_(out) is generally considered to be a constant value.Nonetheless, in one embodiment, V_(out) is determined (e.g., measured orsampled) every n on/off cycles of switch 240, where n is an integer, andthe V_(out) value may be stored and/or updated in power factorcontroller 230 as needed or desired for computing t_(off). At the valuesof V_(out) expected to be observed in certain applications of thepresent disclosure, V_(out) can be measured relatively accurately withrelatively low resolution (at least in comparison with typical values ofI_(in) and/or V_(in) to be detected in the critical mode at inductor 220or feedback current node 234).

Also, as discussed above, t_(on) is a known and/or predetermined valuefor purposes of computing t_(off). However, the voltage V_(in) at node216 is not necessarily a known, predetermined or fixed value at a givenpoint in time during the critical mode of converter operation. V_(in)can be calculated using known, (pre)determined, fixed or reliablymeasurable and/or detectable parameter values, though.

The rectified voltage at node 216 is still a half-sine wave, subject tostandard trigonometric relationships with other parameters. Thus, if oneknows the peak voltage V_(p) at node 216 and the period of the half-sinewave, one can calculate the value of V_(in). Mathematically,

V _(in) =V _(p)*sin(πt/T)   [4]

where t=t_(on) plus the time 330 from t₀ to t_(on), and T is the periodof the rectified voltage half-sine wave (e.g., for a 60 Hz AC powersignal, the period T is 1/(2*60 Hz)=8.3 msec). In one embodiment, powerfactor controller 230 includes one or more counters configured to (i)count the length and/or indicate the end of period T, and/or (ii)determine the length of time t (e.g., initiating a count of known timeincrements in response to an “end of period T” indication and ending thecount at the end of t_(on), when switch 240 is turned off).

As described above, it is generally not desirable to turn switch 240 ontoo soon in the critical mode. However, it is possible to do so whenV_(out) fluctuates (e.g., due to small ripples) and/or when one underdetermines the value of t. As a result, and now referring to FIG. 6, onemay add a small amount of time Δt to t_(off) to provide a kind of bufferagainst turning on switch 240 too soon. Thus, t_(s), the time at whichswitch 240 turns on for a second time in the critical mode, may equalt_(on)+t_(off)+Δt. Alternatively, from the viewpoint of power factorcontroller 230 (see FIG. 4), where t_(off) is the actual length of timethat switch 240 is off in a given on/off cycle,

t _(off) =[t _(on) *V _(in)/(V _(out) −V _(in))]+Δt   [5]

In one embodiment, the transitions between the average current andcritical modes of operation can be determined mathematically. Referringnow to the graph in FIG. 7, two transition periods are shown, one oneach side of the end of voltage half-sine wave period T. The period oftime τ shown in FIG. 7 is effectively the half-period of time in whichboost converter 200 is in the critical mode. The critical mode time iseffectively 2*τ because the voltage half-sine wave and the currentwaveform I is symmetric about the time=T axis. Outside of the time from(T−τ) to (T+τ), boost converter 200 is in the average current mode.

When boost converter 200 is in the critical mode, the current waveform Iintersects the I₀ axis. As a result, t_(s) (which in this embodiment isthe time of the on/off cycle of switch 240; please see FIG. 4) isnecessarily longer than t_(on)+t_(off) (where t_(off) is the time thatit takes current waveform I to reach I₀ when switch 240 is off).Mathematically, referring back to FIG. 6, when (t_(on)+t_(off))<t_(s),then boost converter 200 is in the critical mode. Conversely, when(t_(on)+t_(off))>t_(s), then boost converter 200 is in the averagecurrent mode.

An Exemplary Power Factor Controller

A central aspect of the disclosure relates to a power factor controller,comprising (a) a circuit configured to identify (i) a period of aperiodic power signal and (ii) a length of time from a beginning of theperiod during which a potential is applied to a power conversion switch(e.g., t_(on)); (b) a voltage calculator configured to determine atleast a peak voltage of the periodic power signal; and (c) logicconfigured to calculate a time period to open the switch in response to(i) the length of time, (ii) the power signal period, and (iii) the peakvoltage. Thus, the present power factor controller identifies (i) thepower signal period and (ii) the time length that the power conversionswitch charges the power converter, determines the peak voltage of theperiodic power signal, and calculates a time period during which thepower conversion switch is turned off in response to (1) the “on” timeof the switch, (2) the power signal period, and (3) the peak voltage. Inthe context of the present power factor controller, the term “identify”may refer to receiving and/or providing a predetermined value for thepower signal period and/or the time length t_(on), calculating orcomputing such values from one or more other parameter values, ordetermining such values using conventional techniques for doing so(e.g., counting time increments of predetermined or known length, from aknown initiation or starting point to a known termination or endingpoint). Typically, the periodic power signal comprises an alternatingcurrent power signal or a rectified AC power signal.

In various embodiments, the present power factor controller may furthercomprise (a) a voltage detector configured to determine a zero voltageat an input to the power converter; (b) one or more counters configuredto initiate counting (i) the power signal period and/or (ii) the lengthof time in response to a signal from the voltage detector indicating thezero voltage; (c) a comparator configured to compare the power signalvoltage to a first reference voltage and provide a first relativevoltage value to the voltage calculator; (d) a filter configured toreduce or remove harmonic noise from the power converter output (e.g.,from an output voltage feedback signal); and/or (e) a filter configuredto reduce or remove noise from a current feedback signal.

In other embodiments, the logic comprises a digital signal processor,and/or the logic is further configured to calculate the time period(s)when a power converter comprising the switch is in a critical mode, orapply the potential to the switch for a predetermined period of timewhen a power converter comprising the switch is in a critical mode.Thus, the present power factor controller may process one or moredigital signals (typically a plurality of such signals, as will beexplained in greater detail with regard to FIG. 8). As a result, thepresent power factor controller may further comprise one or more (andtypically a plurality) of analog-to-digital (A/D) converters configuredto convert an analog signal input into the power factor controller to amulti-bit digital signal to be processed by the power factor controllerlogic/digital signal processor. As is known in the art, the number ofbits in an A/D converter corresponds to its resolution; the greater thenumber of bits, the higher the resolution (and the greater the chip realestate, processing power needed, and cost of the power factorcontroller).

FIG. 8 shows an exemplary power factor controller 400 according to thepresent disclosure. Power factor controller 400 generally comprisescomparator block 410, zero voltage crossing locator 412, voltagecalculator 414, input A/D converters 420 and 430, filters 425 and 435,digital signal processor 440 including critical mode controller 416,output digital-to-analog (DIA) converter 445 and output driver 450,which sends a control signal to open or close power conversion switch240 (and if to close switch 240, apply a certain potential to switch240). The disclosure focuses on critical mode controller 416 and theinputs thereto.

Comparator block 410 receives periodic (AC) power signal from AC powerline 212. Given the known relationship between the signal from AC powerline 212 and the rectified version thereof (e.g., rectified AC powersignal 216 in FIG. 4), one skilled in the art can easily perform thecalculations described above from AC power line 212, while avoiding anylatency that may be introduced into the power conversion process byrectifier 210. Comparator block 410 may comprise a comparator block oftwo or more comparators, in which first and second individualcomparators compare the voltage on AC power line 212 with a first andsecond reference voltages, respectively, the first and second referencevoltages being different from one another.

In one implementation, the first comparator in comparator block 410compares the voltage on AC power line 212 with a reference voltagehaving a value of zero volts (0 V), then provides the comparison output411 to zero voltage crossing locator 412, which transmits appropriateinformation and/or control signals to critical mode controller 416 inresponse to the outcome of the comparison. The output 411 from the firstcomparator may be analog or digital, but the output 413 of zero voltagecrossing locator 412 is typically digital. It is well within theabilities of those skilled in the art to design and implement logiccapable of such functions. For example, when output 411 is analog, zerovoltage crossing locator 412 typically comprises an A/D converter andoutput 413 is a multi-bit digital signal carrying information about thevalue of the voltage on AC power line 112 relative to 0 V. However, whenoutput 411 is digital (i.e., the first comparator identifies when the ACvoltage 212 is 0 V or not), zero voltage crossing locator 412 typicallycomprises control logic and output 413 is a single- or multi-bit digitalsignal configured to instruct various circuits and/or logic in criticalmode controller 416 to perform (or stop performing) one or morefunctions in response to the AC voltage 212 being 0 V.

In another implementation, the second comparator in comparator block 410is a conventional peak detector configured to determine the maximumvoltage on AC power line 212 from cycle to cycle (e.g., either AC powersignal cycle or the rectified AC signal half-cycle), then provide anoutput 415 to voltage calculator 414, which transmits appropriateinformation and/or control signals to critical mode controller 416 inresponse to the peak detector output 415. The output 415 from the secondcomparator may be analog or digital, but the output 417 of voltagecalculator 414 is typically digital. It is well within the abilities ofthose skilled in the art to design and implement logic capable of suchfunctions. For example, when output 415 is analog, voltage calculator414 typically comprises an A/D converter and output 417 is a multi-bitdigital signal carrying information about the value of the peak voltageon AC power line 212. However, when output 415 is digital (i.e., thesecond comparator compares the voltage of AC power line 212 to aplurality of reference voltages and provides a multi-bit digital outputidentifying the voltage range that the peak voltage is in), voltagecalculator 414 typically comprises control logic and output 417 is asingle- or multi-bit digital signal configured to instruct variouscircuits and/or logic in critical mode controller 416 to adjust, performor stop performing one or more functions in response to changes in thepeak AC voltage on AC power line 212.

Critical mode controller 416 is configured to compute or calculate atleast two things: the power signal input voltage (e.g., Vin) from thepeak voltage (V_(p)) and the length of time that switch 240 is on in thecritical current mode (t_(on)); and the time period during which switch240 is off (e.g., t_(off) above) when the power converter comprisinginductor 220 (and/or otherwise in electrical communication with switch240) is in the critical mode, from V_(in), V_(out) and t_(on).

Thus, critical mode controller 416 is generally configured to calculateV_(in) from the peak AC voltage on AC power line 212 (provided by output417 from voltage calculator 414), the half-period of the AC power signal(equivalent to the period of the rectified AC power signal and equal tothe time difference between points when the voltage on AC power line212=0 V, information that is provided by output 413 from zero voltagecrossing locator 412), and the time period from when AC voltage on theAC power line 212=0 V to the end of t_(on). As described above, t_(on)is a predetermined length of time that may be programmed into a memoryunit in digital signal processor 440 (or elsewhere in controller 400) orthat may be calculated, computed or determined conventionally by digitalsignal processor 440 in response to one or more appropriate inputs(e.g., a current or voltage input from AC power line 212, a powerconversion feedback from output voltage V_(out) at node 272 and/orfeedback current node 234, etc.).

Digital signal processor 440 also receives (1) a filtered, multi-bitdigital signal from filter 425, corresponding to the power converteroutput voltage feedback signal at node 272, and (2) a filtered,multi-bit digital signal from filter 435, corresponding to the feedbackcurrent node 234. The filter 425 may be a notch filter. These circuitblocks and signals are conventional, and generally perform theirconventional function(s). However, one unexpected advantage of thepresent disclosure is that the A/D converters 420 and 430 (particularly430) can have lower resolution than corresponding A/D converters inconventional boost controllers. This is generally because the presentcomputational approach to minimizing t_(off) does not rely onhigh-resolution information from direct current output V_(out) orfeedback current node 234 to try to measure accurately those periodswhere zero current is flowing through inductor 220. Also as describedabove, one may add a buffer period Δt to t_(off), in part to accommodateor allow for small potential accuracy errors in measuring certainparameters, such as V_(p), V_(out), t, T, and/or (when necessary ordesired) t_(on).

Digital signal processor 440 outputs a multi-bit digital signal to D/Aconverter 445, which converts the multi-bit digital signal to an analogsignal instructing output driver 450 to open or close switch 240. Ifswitch 240 is to be closed, the analog signal received by driver 450informs driver 450 what potential to apply to the gate of switch 240.Alternatively, output driver 450 may comprise a plurality of drivercircuits in parallel, each receiving one bit of the multi-bit digitalsignal output by digital signal processor 440, thereby avoiding a needfor D/A converter 445.

Exemplary Methods

The present disclosure further relates to method of controlling a powerconverter, comprising the steps of (a) storing energy from a periodicpower signal in the power converter in response to application of apotential to switch in electrical communication with the powerconverter; (b) calculating a time period to open the switch (e.g.,t_(off)) from (i) an initial length of time during which a potential isapplied to the switch (e.g., t_(on)), (ii) a period of the periodicpower signal (e.g., T), and (iii) a peak voltage of the periodic powersignal (e.g., V_(p)); and (c) opening the switch during the time period.As for the descriptions of hardware above, the periodic power signal maycomprise an alternating current power signal or a rectified AC powersignal, depending on design choices and/or considerations. The energy istypically stored in an inductor when a current from a rectified AC powersignal passes through the inductor, and current generally passes throughthe inductor when the switch is closed. Energy typically is not storedin the boost converter (inductor) when the switch is open.

In various embodiments, the method may further comprise the step(s) of:(1) determining a zero voltage at an input to the power converter; (2)timing, or identifying or determining a time length for, (i) the powersignal period and/or (ii) the length of time in response to a zerovoltage indication; (3) determining the peak voltage of the periodicpower signal; (4) calculating the time period or otherwise identifyingwhen the power converter is in a critical mode; (5) filtering harmonicnoise from an output of the power converter; and/or (6) filtering noisefrom a current feedback signal. Each of these additional steps isgenerally performed as described above with respect to the correspondinghardware configured to conduct, practice or implement the step.

In certain implementations, the step of determining the peak voltage maycomprise comparing a voltage of the periodic power signal to a firstreference voltage, sampling an output of the comparing step to generatea plurality of power signal voltage samples, and determining a maximumpower signal voltage sample value, the peak voltage corresponding to themaximum power signal voltage sample value. Also, the present methodgenerally further comprises the step of applying a potential to theswitch for a predetermined period of time when the power converter is inthe critical mode.

Exemplary Software

The present disclosure also includes algorithms, computer program(s)and/or software, implementable and/or executable in a general purposecomputer or workstation equipped with a conventional digital signalprocessor, configured to perform one or more steps of the method and/orone or more operations of the hardware. Thus, a further aspect of thedisclosure relates to algorithms and/or software that implement theabove method(s). For example, the disclosure may further relate to acomputer program, computer-readable medium or waveform containing a setof instructions which, when executed by an appropriate processing device(e.g., a signal processing device, such as a microcontroller,microprocessor or DSP device), is configured to perform theabove-described method and/or algorithm.

For example, the computer program may be on any kind of readable medium,and the computer-readable medium may comprise any medium that can beread by a processing device configured to read the medium and executecode stored thereon or therein, such as a floppy disk, CD-ROM, magnetictape or hard disk drive. Such code may comprise object code, source codeand/or binary code.

The waveform is generally configured for transmission through anappropriate medium, such as copper wire, a conventional twisted pairwireline, a conventional network cable, a conventional optical datatransmission cable, or even air or a vacuum (e.g., outer space) forwireless signal transmissions. The waveform and/or code for implementingthe present method(s) are generally digital, and are generallyconfigured for processing by a conventional digital data processor(e.g., a microprocessor, microcontroller, or logic circuit such as aprogrammable gate array, programmable logic circuit/device orapplication-specific [integrated] circuit).

In various embodiments, the computer-readable medium or waveformcomprises at least one instruction (or subset of instructions) to (a)count predetermined time units corresponding to (i) the power signalperiod and/or (ii) the length of time, in response to an indication of azero voltage on the periodic power signal; (b) determine (e.g., computeor calculate) the peak voltage; and/or (c) determine and/or indicate(e.g., by calculating a corresponding time period) when the powerconverter is in the critical mode. In one implementation, theinstruction(s) to determine the peak voltage comprise at least onesubset of instructions to (i) sample an output of a comparison of theperiodic power signal voltage to a reference voltage, (ii) store aplurality of power signal voltage samples, and (iii) determine a maximumpower signal voltage sample value, the peak voltage corresponding to themaximum power signal voltage sample value.

Thus, the present disclosure provides a circuit, system, method andsoftware for controlling a power conversion and/or correcting and/orcontrolling a power factor in such conversion(s). The circuitrygenerally comprises a power factor controller, comprising (a) a circuitconfigured to determine and/or identify (i) a period of a periodic powersignal and (ii) a length of time from a beginning of the period duringwhich a potential is applied to a power conversion switch; (b) a voltagecalculator configured to determine at least a peak voltage of theperiodic power signal; and (c) logic configured to calculate a timeperiod to open the switch in response to (i) the length of time, (ii)the power signal period, and (iii) the peak voltage. The systemgenerally comprises the present power factor controller and a switchthat it controls, although the system aspect of the disclosure alsorelates to a power converter comprising the present power factorcontroller, the switch, and an inductor configured to store energy fromthe periodic power signal.

The method generally comprises the steps of (1) storing energy from aperiodic power signal in a power converter in response to application ofa potential to switch in electrical communication with the powerconverter; (2) calculating a time period to open the switch from (i) aninitial length of time during which a potential is applied to theswitch, (ii) a period of the periodic power signal, and (iii) a peakvoltage of the periodic power signal; and (3) opening the switch duringthe time period. The software generally comprises a set of instructionsadapted to carry out the present method.

The present disclosure generally takes a computational approach toreducing and/or minimizing zero current periods in the critical mode ofpower converter operation, and advantageously reduces zero currentperiods in the critical mode to a reasonable and/or tolerable minimum,thereby maximizing the power factor of the power converter in thecritical mode and reducing noise that may be injected back into AC powerlines. The present power factor controller allows for greater designflexibility, reduced design complexity, and/or reduced resolution and/orgreater tolerance for error in certain parameter measurements orsamples.

Referring now to FIG. 9, an alternate power factor control module 500switches modes of the boost converter. In some implementations, thepower factor control module 500 may switch the mode from continuous modeto discontinuous mode and/or from discontinuous mode to continuous modeduring zero-crossings of the powerline input signal.

The power factor control module 500 includes a phase detecting module504, which determines a phase θ of the input signal. The phase detectingmodule 504 may include a zero-crossing module 508 that detectszero-crossings of a voltage of the input signal. The phase detectingmodule 504 may determine the phase θ of the input signal based on thezero-crossings. In other words, the phase θ of the input signal may be0° or 180° when the zero-crossings occur. The phase θ of the inputsignal may also be determined based on a peak voltage of the inputsignal, which may occur at 90° and 270°.

Likewise, the period T of the input signal may be determined by thephase detecting module 504. In other words, one-half of the period T ofthe input signal may be equal to a period between two adjacentzero-crossings or between two voltage peaks. Alternately, the period Tmay be set to a constant value if known.

The power factor control module 500 may further comprise a peak voltagedetermining module 512 that determines a peak voltage of the inputsignal. The peak voltage determining module 512 may sample and hold theinput voltage to identify the peak voltage. In other words, the sampleand hold continues until the sampled value decreases relative to apreceding value. Other techniques may be used to identify timing and/ormagnitude of the peak voltage. The peak voltage determining module 512may output the peak voltage V_(P) to the phase detecting module 504 tohelp estimate the phase θ of the input signal.

The power factor control module 500 may further comprise a switchcontrol module 516 that controls a state of the switch and a switchingfrequency of the switch. The phase detecting module 504 may output theperiod T, the phase θ and/or zero-crossing signals of the powerlineinput signal to the switch control module 516. The peak voltagedetermining module 512 may output peak voltage signals V_(P) such asmagnitude and/or timing of the powerline input signal to the switchcontrol module 516.

The switch control module 516 may further comprise a mode control module520 that selects a mode of the boost converter. For example, the modemay be set to a continuous mode, a discontinuous mode or a criticalmode. The mode control module 520 may also be arranged outside of theswitch control module 516 and/or combined with another module of thepower factor control module 500.

The mode control module 520 may select the mode and determine whether toswitch modes based on sensed operating parameters. For example only, themode control module 520 may determine when to switch the mode from thecontinuous mode to the discontinuous mode or from the discontinuous modeto the continuous mode based on the zero-crossing signals. For exampleonly, the switching may be done within a predetermined period of apowerline zero-crossing. However, the switching between modes may alsooccur at different phase locations of the powerline input signal (inaddition to or instead of switching at zero-crossing of the voltage ofthe powerline input signal). Switching from the continuous mode ordiscontinuous mode to the critical mode may also be done at these times.

The mode control module 520 may generate a control signal for switchingthe mode from the continuous mode to the discontinuous mode or from thediscontinuous mode to the continuous mode based on the zero-crossingsignals, phase and/or other sensed operating parameters, such as,current and voltage. Based on the selected mode, the switch controlmodule 516 also selects the frequency of the switch.

The switch control module 516 may include an on-time module 524 thatsets an on-time period t_(on) for the switch 240 as described herein.The on-time period t_(on) may be a constant value or adjustable. Theswitch control module 516 may include an off-time module 528 that setsan off-time period t_(off) for the switch 240 as described herein.

Referring now to FIG. 10A, a method 550 for adjusting a switchingfrequency of the boost converter begins with step 552. In step 554,control determines whether there has been a requested operating modechange. If step 554 is false, control returns to step 554. If step 554is true, control continues with step 554 and determines whether thecontinuous mode has been selected. If true, control sets the switchingfrequency greater than the critical frequency f_(c) in step 560.

If step 554 is false, control determines whether the discontinuous modehas been selected in step 564. If step 564 is true, control sets theswitching frequency f_(c) less than the critical frequency in step 568.If step 564 is false, control defaults to the critical mode and sets theswitching frequency equal to the critical frequency f_(c) in step 572.

As can be appreciated, the switching between modes can be performed atany time. In some implementations, the switching frequency can be set asshown in FIG. 10A and switching is performed at any time during thecycle of the power input signal. In some implementations, the switchingfrequency can be set as shown in FIG. 10A and switching is performed atvoltage zero crossings as shown in FIG. 10B.

Referring now to FIG. 10B, a method 600 switching modes of the boostconverter at voltage zero crossings begins at step 602. The mode controlmodule may select a mode (e.g., the continuous mode, the critical modeor the discontinuous mode) in step 606 based on operating conditionssuch as V_(out), load conditions and/or other operating parameters.Control determines in step 608 whether the mode control module 520requests a mode change. For example, the mode may change from one of thecontinuous mode, the critical mode or the discontinuous mode to anotherone of the continuous mode, the critical mode or the discontinuous mode.

In step 610, the mode control module 520 determines whether thezero-crossing module 508 detects a zero-crossing. If the result of step610 is false, the mode control module 520 waits until the zero-crossingmodule detects a zero-crossing. If the result of step 610 is true, themode control module 520 switches the mode to the selected mode in step614.

The switching frequency in the continuous mode may be greater than theswitching frequency in the discontinuous mode. Specifically, theswitching frequency in the continuous mode may be determined based onfactors including a power rating of the boost converter, the estimatedload, and values of components (for example only, the inductor 220 andthe capacitor/filter 260).

For example only, the switching frequency in the continuous mode may bebetween 500 KHz and 2 MHz. For example only, the switching frequency inthe continuous mode may be 1 MHz. The switching frequency indiscontinuous mode may be based on or proportional to the estimated loadcurrent.

Referring now to FIG. 11, the switch control module 516 may set theswitching frequency based on a phase and/or other parameters of thepowerline input signal. Specifically, the switching frequency may begreater than a critical or boundary switching frequency f_(c) incontinuous mode and may be less than the critical switching frequencyf_(c) in discontinuous mode. The critical switching frequency f_(c) maybe given by the following formula:

f _(c)=0.25*(V _(p) ²)*(1−V _(p)*sin(θ)/V _(o))/(P _(o) *L)

where V_(p)=1.44*V_(RMS) is a peak value of the voltage of the powerlineinput signal (e.g., V_(p)=144 volts when V_(RMS)=110 volts), V_(o) is anoutput voltage of the boost converter, P_(o) is an output power of theboost converter, L is an inductance, and θ is the phase of the powerlineinput signal.

A maximum value of the critical switching frequency f_(c) may be givenby the following formula.

f _(max)=0.25*(V _(p) ²)/(P _(o) *L).

Accordingly, the critical switching frequency f_(c) may be expressed asa product of f_(max) and a frequency ratio f_(ratio) as follows.

f _(c) =f _(max) *f _(ratio)

where f_(ratio) is a ratio of the switching frequency to the maximumvalue of the critical switching frequency and is given by

f _(ratio)=(1−V _(p)*sin(θ)/V _(o)).

The foregoing descriptions of specific embodiments of the presentdisclosure have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit thedisclosure to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the disclosure and its practical application,to thereby enable others skilled in the art to best utilize thedisclosure and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the disclosure be defined by the Claims appended hereto and theirequivalents.

1. A boost converter, comprising: an inductance that receives an inputsignal; a switch that controls current supplied via said inductance to aload; and a power factor control module comprising: a mode controlmodule that selects an operating mode of said boost converter; and aswitch control module that switches said switch at a switchingfrequency, that sets said switching frequency equal to a first frequencywhen said mode control module selects a continuous mode and that setssaid switching frequency equal to a second frequency when said modecontrol module selects a discontinuous mode, wherein said firstfrequency is different from said second frequency.
 2. The boostconverter of claim 1 wherein said first frequency is greater than saidsecond frequency.
 3. The boost converter of claim 1 wherein said switchcontrol module determines said switching frequency independently ofmeasurement of current through said inductance.
 4. The boost converterof claim 1 wherein the power factor control module further includes: aphase detecting module that determines a period of said input signal; apeak voltage determining module that senses a peak voltage of said inputsignal; and an on-time module that provides an on-time of said switch.5. The boost converter of claim 3 wherein the power factor controlmodule further comprises an off-time module that calculates an off-timeof said switch based on said period, said on-time and said peak voltage.6. The boost converter of claim 4 wherein said off-time modulecalculates said off-time independently of measurement of current flowingthrough said inductance.
 7. The boost converter of claim 4 wherein thephase detecting module comprises a zero-crossing module that detectszero-crossing of a voltage of said input signal.
 8. The boost converterof claim 7 wherein said mode control module controls transitions betweensaid discontinuous mode and said continuous mode based on saidzero-crossing.
 9. The boost converter of claim 4 wherein said phasedetecting module further determines a phase of said input signal. 10.The boost converter of claim 9 wherein said first frequency is greaterthan a boundary frequency and said second frequency is less than saidboundary frequency, and wherein said boundary frequency is based on saidphase of said input signal.
 11. The boost converter of claim 10 whereinsaid boundary frequency is based on:f _(c)=0.25*(V _(p) ²)*(1−V _(p)*sin(θ)/V _(o))/(P _(o) *L) where f_(c)is said boundary frequency, θ is said phase, V_(p) is a peak voltage ofsaid input signal, V_(o) is an output voltage of said boost converter,P_(o) is an output power of said boost converter, and L is a value ofsaid inductance.
 12. The boost converter of claim 10 wherein saidboundary frequency is based on a peak value of said input signal, anoutput power of said boost converter, and a value of said inductance.13. The boost converter of claim 10 wherein said boundary frequency is aproduct of a maximum boundary frequency and a first value, wherein saidmaximum boundary frequency is based on said peak voltage of said inputsignal, an output power of said boost converter, and a first inductancevalue of said inductance and wherein said first value is based on saidpeak voltage of said input signal and said output power of said boostconverter.
 14. A power factor controller, comprising: a mode controlmodule that selects an operating mode of a power converter; and a switchcontrol module that switches a switch at a switching frequency tocontrol a current, that sets said switching frequency equal to a firstfrequency when said mode control module selects a continuous mode andthat sets said switching frequency equal to a second frequency when saidmode control module selects a discontinuous mode, wherein said firstfrequency is different from said second frequency, and wherein saidswitch control module determines said switching frequency independent ofmeasurement of current through an inductance.
 15. The power factorcontroller of claim 14 wherein said first frequency is greater than saidsecond frequency.
 16. The power factor controller of claim 14, whereinthe current is supplied via the inductance to a load, the power factorcontroller further comprising: a phase detecting module that determinesa period of an input signal received by said inductance; a peak voltagedetermining module that senses a peak voltage of said input signal; andan on-time module that provides an on-time of said switch.
 17. The powerfactor controller of claim 16 further comprising an off-time calculatingmodule that calculates off-time of said switch based on said period,said on-time and said peak voltage.
 18. The power factor controller ofclaim 16 wherein the phase detecting module comprises a zero-crossingmodule that detects zero-crossing of a voltage of said input signal. 19.The power factor controller of claim 18 wherein said mode control modulecontrols transitions between said discontinuous mode and said continuousmode based on said zero-crossing.
 20. The power factor controller ofclaim 16 wherein said phase detecting module determines a phase of saidinput signal.
 21. The power factor controller of claim 20 wherein saidfirst frequency is greater than a boundary frequency and said secondfrequency is less than said boundary frequency, and wherein saidboundary frequency is based on said phase of said input signal.
 22. Thepower factor controller of claim 21 wherein said boundary frequencyf_(c) is based on:f _(c)=0.25*(V _(p) ²)*(1−V _(p)*sin(θ)/V _(o))/(P _(o) *L) where f_(c)is said boundary frequency, θ is said phase, V_(p) is a peak voltage ofsaid input signal, V_(o) is an output voltage of said power converter,P_(o) is an output power of said power converter, and L is a value ofsaid inductance.
 23. The power factor controller of claim 21 whereinsaid boundary frequency is based on a peak value of said input signal,an output power of said power converter, and a value of said inductance.24. The power factor controller of claim 21 wherein said boundaryfrequency is based on a maximum boundary frequency and a first value,wherein said maximum boundary frequency is based on said peak voltage ofsaid input signal, an output power of said power converter, and a firstinductance value of said inductance, and wherein said first value isbased on said peak voltage of said input signal and said output power ofsaid power converter.
 25. A method for operating a boost converter,comprising: controlling current supplied via an inductance to a loadwith a switch; selecting an operating mode of said boost converter;switching said switch at a switching frequency; setting said switchingfrequency equal to a first frequency when operating in a continuousmode; and setting said switching frequency equal to a second frequencywhen operating in a discontinuous mode, wherein said first frequency isdifferent from said second frequency.
 26. The method of claim 25 whereinsaid first frequency is greater than said second frequency.
 27. Themethod of claim 25 further comprising determining said switchingfrequency independently of measurement of current through saidinductance.
 28. The method of claim 25 further comprising: determining aperiod of an input signal; sensing a peak voltage of said input signal;and providing an on-time of said switch.
 29. The method of claim 28further comprising calculating an off-time of said switch based on saidperiod, said on-time and said peak voltage.
 30. The method of claim 29wherein said off-time is calculated independently of measurement ofcurrent flowing through said inductance.
 31. The method of claim 28further comprising detecting zero-crossing of a voltage of said inputsignal.
 32. The method of claim 31 further comprising: controllingtransitions between said discontinuous mode and said continuous modebased on said zero-crossing.
 33. The method of claim 28 furthercomprising detecting a phase of said input signal.
 34. The method ofclaim 33 wherein said first frequency is greater than a boundaryfrequency and said second frequency is less than said boundaryfrequency, and wherein said boundary frequency is based on said phase ofsaid input signal.
 35. The method of claim 34 wherein said boundaryfrequency is based on:f _(c)=0.25*(V _(p) ²)*(1−V _(p)*sin(θ)/V _(o))/(P _(o) *L) where f_(c)is said boundary frequency, θ is said phase, V_(p) is a peak voltage ofsaid input signal, V_(o) is an output voltage of said boost converter,P_(o) is an output power of said boost converter, and L is a value ofsaid inductance.
 36. The method of claim 34 wherein said boundaryfrequency is based on a peak value of said input signal, an output powerof said boost converter, and a value of said inductance.
 37. The methodof claim 34 wherein said boundary frequency is a product of a maximumboundary frequency and a first value, wherein said maximum boundaryfrequency is based on said peak voltage of said input signal, an outputpower of said boost converter, and a first inductance value of saidinductance and wherein said first value is based on said peak voltage ofsaid input signal and said output power of said boost converter.
 38. Amethod for operating a power factor controller, comprising: selecting anoperating mode of a power converter; and switching a switch at afrequency to control current supplied via an inductance to a load;setting said switching frequency equal to a first frequency when acontinuous mode is selected as the operating mode; and setting saidswitching frequency equal to a second frequency when a discontinuousmode is selected as the operating mode, wherein said first frequency isgreater than said second frequency, and wherein said switching frequencyis determined independent of measurement of current through saidinductance.
 39. The method of claim 38 further comprising: determining aperiod of an input signal received by said inductance; sensing a peakvoltage of said input signal; and providing an on-time of said switch.40. The method of claim 39 further comprising calculating off-time ofsaid switch based on said period, said on-time and said peak voltage.41. The method of claim 39 further comprising detecting zero-crossing ofa voltage of said input signal.
 42. The method of claim 41 furthercomprising: controlling transitions between said discontinuous mode andsaid continuous mode based on said zero-crossing.
 43. The method ofclaim 39 further comprising detecting a phase of said input signal. 44.The method of claim 43 wherein said first frequency is greater than aboundary frequency and said second frequency is less than said boundaryfrequency, and wherein said boundary frequency is based on said phase ofsaid input signal.
 45. The method of claim 44 wherein said boundaryfrequency f_(c) is based on:f _(c)=0.25*(V _(p) ²)*(1−V _(p)*sin(θ)/V _(o))/(P _(o) *L) where f_(c)is said boundary frequency, θ is said phase, V_(p) is a peak voltage ofsaid input signal, V_(o) is an output voltage of said power converter,P_(o) is an output power of said power converter, and L is a value ofsaid inductance.
 46. The method of claim 44 wherein said boundaryfrequency is based on a peak value of said input signal, an output powerof said power converter, and a value of said inductance.
 47. The methodof claim 44 wherein said boundary frequency is based on a maximumboundary frequency and a first value, wherein said maximum boundaryfrequency is based on said peak voltage of said input signal, an outputpower of said power converter, and a first inductance value of saidinductance, and wherein said first value is based on said peak voltageof said input signal and said output power of said power converter.